(a) Field of the Invention
The present invention relates to a method of calculating a log-likelihood ratio and a method of detecting a transmission signal. More particularly, the present invention relates to a method of calculating a log-likelihood ratio and a method of detecting a transmission signal in a multiple input multiple output (MIMO) system using a spatial multiplexing (SM) method.
(b) Description of the Related Art
Future mobile communication systems demand high-speed data transmission under stationary and mobile environments. In order to meet these demands, a multiple input multiple output (MIMO) system using a spatial multiplexing (SM) method that is capable of transmitting a multiple data layer is attracting attention.
In the MIMO system using the spatial multiplexing method, a data layer indicating different information is transmitted through a transmitting antenna, and a receiving terminal separates the transmitted data layers. In the data layer separation method according to the related art, maximum likelihood (ML) bit metric detection has been used in which a maximum likelihood metric is calculated for each of transmission symbol vectors that can be combined and a transmission symbol vector having the smallest ML metric is searched, in order to perform optimal transmission symbol detection.
However, even though the ML bit metric detection provides optimal transmission symbol detection performance, since hardware complexity is exponentially increased with respect to the size of a constellation and the number of transmitting antennas, the ML bit metric detection has a drawback in that extremely high complexity is required.
Meanwhile, methods such as maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD) and likelihood ratio logarithm with QR decomposition and M-algorithm (QR-LRL), which are new detecting methods, have been proposed to solve this problem. If these methods are used, the hardware complexity is decreased. However, there is a problem in that the calculation of the log-likelihood ratio becomes inaccurate because the number of candidate vectors used in calculating the log-likelihood ratio is small.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.